A ring oscillator may comprise multiple delay stages or cells configured to generate a self-sustaining oscillating signal with an operating frequency. An injection locked oscillator (ILO) is one type of ring oscillator that tracks its operating frequency to an input reference clock. ILOs can be used for various purposes such as frequency multiplication, frequency division, and clock generation. An ILO may have a high input tracking bandwidth, which helps rejecting a bias noise while providing a low-noise and multi-phase clock. The multi-phase clock may be needed by phase rotators in a digital clock and data recovery (CDR) device, e.g., to sample and track received data.
In modern devices, to fit various applications, ring oscillators may be designed to cover a wide frequency tuning range (e.g., from 2 gigahertz (GHz) to 7.5 GHz or higher). One challenge in the design of such ring oscillators is to cover a wide frequency range with sufficient amplitude and low phase noise, while minimizing power and area overhead.